Patent GB-1044270-A (GB)
Title: Multistable electronic circuit
IPC: H03K3/29
Filed: 1964-12-14
Abstract: 1,044,270. Multi-stable circuits. INTERNATIONAL BUSINESS MACHINES CORPORATION. Dec. 14, 1964 [Dec. 30, 1963], No. 50720/64. Heading H3T. [Also in Division G4] A multi-stable circuit includes two regeneratively coupled transistors to provide two stable states with one cut off and the other fully conducting and vice versa, and one or more intermediate states stabilized by degenerative feedback loops. Fig. 3 shows a five-stable circuit initially in one extreme state with transistor 94 fully conducting and 96 cut off, the potentials at points 172 and 178 being - 6 V. and that at 186 being - 12 V. If the potential at 172 is increased to + 6 V. and that at 186 to zero, the circuit will pass successively through its stable states to the other extreme with transistor 96 fully conducting and 94 cut off. Reversion of the input potentials to their former values at any time during the transition will maintain the circuit in the nearest stable intermediate state. State 1 to State 2.-The rise of voltage at 172 cuts off diode 170 and the potential at 180 starts to rise, carrying the base of 94 with it. Transistor 96 starts to conduct by regeneration (a) from the emitter of 94 to the emitter of 96 through diode 34; and (b) from the collector of 94 to the base of 96 through resistors 114 and 116. When the collector of 94 reaches the potential of point 124 diode 126/1 conducts in addition to 126/2 and clamps the base and collector of 94 together to prevent further change. State 2 to State 3.-Further rise in the base potential of 94 cuts off diode 126-1 and the transistor current starts to fall again. When the two transistors become nearly equal in conduction, diode 34 cuts off and the regeneration through path (b) alone is insufficient to cause further change. State 3 to State 4.-Further rise in the collector potential of 96 brings it up to that of point 154, when diode 156/2 conducts in addition to 156/1 and clamps the base and collection of 96 together. State 4 to State 5.-Further rise in the collector potential of 96 cuts off diode 156-2 and 96 conducts fully, 94 now being cut off. Operational details.-Capacitor 162 prevents overshoot of either base potential beyond its stable value, and also serves to store pulses which are too small in amplitude to trigger the circuit until their integrated value is sufficient. The circuit can be reset to state 3 by momentarily raising the potential of point 110. Output signals are taken from points 194 and 196. Modifications.-By omitting resistors 182, 190 and replacing diodes 170, 176 by capacitors (Fig. 4, not shown) the circuit will change only from one state to the next irrespective of the length of the input pulse since this will be differentiated by the capacitor. The number of diode pairs 126, 156 can be increased to provide extra stable states, and the state provided by diodes 34, 36 can be omitted (Fig. 2, not shown). The number of diode pairs associated with transistor 94 may be different from that associated with transistor 96. The output voltage change in going from one state to another can be varied by altering the appropriate resistance values and these changes can be unsymmetrical in degree about the centre state. Additional circuit.-A circuit is described (Fig. 1, not shown) which does not form part of the invention. This is similar to Fig. 3 but omits the diode pairs 126, 156 and thus has only three stable states. The collector loads 106, 108 can be replaced by lamps whose brilliance indicates the state of the circuit. The capacitor 162 is replaced by two separate capacitors coupling the base and emitter of each transistor degeneratively. This circuit can be triggered by single inputs at 172 or 178 by holding the potential of 186 at zero volts.